1. Technical Field
The present disclosure is directed to a methodology and device/system for quick (e.g., 10-30 min) benchtop tests of the effectiveness of magnetic treatment of feed water for reducing mineral scaling on a reverse osmosis (RO) membrane.
2. Background Art
Water shortage is one of the most urgent global challenges in the 21st century. The population growth and shifting, industrialization, contamination of available freshwater resources, and climate change exacerbate water shortages and safety in various arid and even high-rainfall regions worldwide. The needs to meet greater societal future demands and ecological benefits have long motivated research and developments for a solution to water scarcities. The only methods incorporated successfully to provide additional fresh water production beyond what is available from the hydrological cycle are the desalination and water reuse. Although costs of water reuse from rivers and groundwater, recycled water, and water conservation are lower than those of desalinated water, these portable water sources are not always available, whereas desalination offers a seemingly unlimited, steady supply of high-quality water, without impairing natural freshwater ecosystems.
Desalination is the process of removing salt from seawater or brackish water to produce fresh water. Reverse osmosis (RO) is the major membrane-based technology for desalination because of its efficiency. It is a pressure-driven process in which an applied pressure is used to overcome the osmotic pressure whereby a semi-permeable membrane lets solvents pass through but rejects ions in the feed water. RO has emerged as the leader in future desalination installations due to a smaller amount of energy consumption that is several times smaller than that of other technologies. RO is considered to be the key to increasing water supplies for drinking water production worldwide [1].
RO systems for production of drinking water from seawater and saline aquifers has advanced significantly in the past decade, owing to the development of more robust membranes and efficient energy recovery methods [1-4]. However, membrane fouling remains among the major RO challenges. Sparingly soluble salts in feed water can crystallize directly onto the RO membrane surface, forming an adherent mineral scale that causes the permeate flux to decline and eventually damages the membrane.
The most widespread strategy employed to reduce membrane fouling is the use of antiscalant additives to the feed water that can inhibit the nucleation and growth of scale deposits. However, chemical cleaning is not free from hazards and facilitates metallic corrosion and biofouling by microorganism colonies. Moreover, chemical treatments are highly specific to a particular composition of the feed water with respect to their effectiveness and may substantially affect the composition of drinking water. Environmental and regulatory agencies frequently object to disposal of antiscalant and biocidal chemicals present in concentrate (marine, brackish, wastewater). These chemicals also complicate beneficial product recovery and increase operating costs of RO desalting.
There are a host of currently-marketed technologies which use combinations of magnetic, electrostatic, and electromagnetic fields for treatment of feed water. These technologies are compelling due to their simplicity and relatively low cost. Magnetic and/or electrical-based conditioners of feed water are available in a wide variety of configurations, and can be plumbed in or clamped on. They are sold worldwide and claimed to suppress scale formation, increase membrane lifetime, and replace feed treatment with chemicals.
A majority of marketed devices use magnetic water treatment employing an array of permanent magnets or electromagnets. The history of magnetic water treatment in various applications is long and controversial, marked by claims for and against their effectiveness.
Most studies published in the open literature reviewed in Refs. [5]-[7] are focused on testing of anti-scale magnetic treatment of water in heating systems and RO and nanofiltration processes for producing drinking water. While many publications claimed no significant effects of magnetic treatment, many publications considered to be sufficiently credible demonstrated that the magnetic treatment facilitated reduction of scale deposition or removal of scale or appearance of softened deposits that were easier to remove. Furthermore, the treatment influence was reported to last up to hundreds hours after a field had ceased. Benefits of magnetic treatment were found to depend strongly on various operating parameters, such as field strength and direction with respect to the flow, exposure time, temperature, channel geometry and flow rate, water composition, and pH level. Several hypotheses are typically invoked to explain the efficiency of magnetic treatment of water in the technical literature [8-20]. It is usually agreed that magnetic treatment facilitates bulk precipitation of sparingly soluble salts in feed water, thereby suppressing formation of a tightly adherent scale layer.
Given the widespread availability of inexpensive magnetic and electrical based water conditioners advertised for replacement of chemical treatment of water, it is expected that such devices will continue to draw interest across the industry to explore whether they are efficient in a particular RO system. Due to the high costs of tests on large RO units, it is an urgent need to develop a benchtop test for evaluating whether a particular electro-magnetic treatment can be useful under specific operating conditions of a large industrial RO system and further large-scale testing effort of this technique is warranted.
The present disclosure presents an advantageous method and benchtop device for quickly testing the effectiveness of a water conditioner that is claimed to improve the lifetime efficiency of a large industrial RO system. These and other needs are addressed by the methods and devices/systems of the present disclosure.